Catch LogCat programmatically or export it to file

UPDATE - THIS POST IS VALID ONLY FOR API < 16 (ANDORID 4.1 JELLY BEAN), OTHERWISE YOU NEED ROOT PERMISSION 

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Let'see how to catch LogCat from code.
It's very simple, just remember how to call it, and read his input stream.


LogCat process can be launched with parameters such as -help for help,
-s for silent filter,
-d for dump
-c for clear and,
-f for file export.

The (Nyan)LogCat

Those parameters can be combined together.
If you don't specify -s (or *:S) you'll see the entire log.

-s stands for silent, LogCat will print informations only from "myTag".

String myCommand="logcat -s myTag";
Process process = Runtime.getRuntime().exec(myCommand);

BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));

StringBuilder log=new StringBuilder();
String line = "";

while ((line = bufferedReader.readLine()) != null) 
{
        log.append(line);
        //handler.sendMessage(...); bring message to mainThread
}

You can print more tags at time and specify for each tag which level of log needs priority.

String myCommand="logcat myTag *:S"; //the equivalent of logcat -s myTag
myCommand="logcat -s myTag:D"; //priority to 'debug level' for myTag
myCommand="logcat -s myTag:E myTag2:D"; //priority to 'error level' for myTag and 'debug level' for myTag2, nothing else is showed
myCommand="logcat myTag:E myTag2:D"; //priority to 'error level' for myTag and 'debug level' for myTag2, everything is showed

Remember if you don't specify -d logcat will keep printing log.

If you only need to export a logcat file, you can use -f parameter and specify output path. For example:

String myCommand="logcat -f /sdcard/output.txt"; //no filters, keep writing
myCommand="logcat -d -f /sdcard/output.txt"; //no filters, just a dump

I recommend this notation that can be combined with a filter:

myCommand="logcat -d myTag:V *:S > /sdcard/output.txt"; 
//write a dump for myTag (lever verbose) ,nothing else

Here the official reference for adb and LogCat.